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What is a Sleeper Shark?

J.L. Drede
J.L. Drede

The sleeper shark is a family of sharks known by its scientific name somniosidae. There are many different species of sleeper shark but two most well-known are the Pacific sleeper shark and the Greenland shark. Other sleeper sharks are commonly referred to as dogfish.

The Pacific sleeper shark has a wide habitat range and has been spotted in seas around the arctic, Japan, Australia and throughout most of the pacific. It is large, with specimens at least 23 feet (7 meters) having been seen in the wild. Not much is known about the shark, as it is a deep sea shark rarely spotted near the surface. Like many other fish who live on the ocean floor, it is slow-moving and has adapted to survive in extremely cold weather, as low as 40 degrees Fahrenheit (4 Celsius). It hunts live prey, and has a mouth that is specially designed to tear large chunks of flesh to devour whole. The stomach contents of deceased pacific sleeper sharks show a diverse palette; dolphins, snails, crabs and seals all seem to be prey for the massive fish. There is also evidence to suggest that the pacific shark even hunts giant squid, making them and the sperm whale the only known predators of that giant creature.

Stomach contents of beached Greenland sharks have been found to contain the remains of animals such as polar bears.
Stomach contents of beached Greenland sharks have been found to contain the remains of animals such as polar bears.

The Greenland sleeper shark is closely related to the pacific variety, and is similar in size. It too can grow upwards of 20 feet (6 meters) in length, and often weighs more than 2,200 pounds (1,000 kilograms). It too is also comfortable in extreme weather and depths. It has been found at depths as low as 7,200 feet (2,200 meters). Like its name suggests the Greenland sleeper shark is native to the Greenland area, and is also found along the shores of upper North America and in parts of Europe. Stomach contents of captured or beached Greenland sharks have been found to contain the remains of polar bears, seals, horses and squid.

While it was once believed that the shark was primarily a scavenger eater that feasted on the remains of dead animals, researchers have since witnessed firsthand the massive shark attacking live caribou and other large animals.

Dolphins sometimes fall prey to Pacific sleep sharks.
Dolphins sometimes fall prey to Pacific sleep sharks.

Greenland sleeper shark is considered to be a delicacy in both Greenland and Iceland, but it must be prepared carefully as the flesh of the shark is poisonous. Typical preparation of Greenland shark involves it being boiled several times over until the poison is removed. It is also often left hanging in barns for months, where it can dry and ferment. This process can last several months. The final result is a dish called hakari, which is known for its incredibly strong taste that has caused violent reactions in those not used to it.

Frequently Asked Questions

What is a sleeper shark, and where can it be found?

Squid are often found in the stomach contents of beached Greenland sharks.
Squid are often found in the stomach contents of beached Greenland sharks.

Sleeper sharks are a group of deep-sea shark species known for their sluggish behavior and preference for cold waters. They inhabit the Atlantic, Pacific, and Arctic Oceans, often dwelling at depths of 2,000 meters or more. Notably, the Greenland shark, a type of sleeper shark, is found in the North Atlantic and Arctic Oceans.

How large can sleeper sharks grow?

Sleeper sharks exhibit considerable size variation among species. The Greenland shark, one of the largest species, can grow up to 7 meters in length and weigh over 1,000 kilograms. These sharks grow slowly and can live for centuries, with some estimates suggesting a lifespan of up to 400 years for the Greenland shark.

What do sleeper sharks eat?

Sleeper sharks have a diverse diet, feeding on fish, squid, and even marine mammals. Their slow-moving nature belies their effectiveness as predators, often ambushing prey or scavenging on carrion. The Greenland shark, for example, has been known to consume seals and has even been found with remains of polar bears and reindeer in its stomach.

Are sleeper sharks dangerous to humans?

Sleeper sharks, due to their deep-sea habitat and lethargic nature, rarely encounter humans and are not considered a significant threat. There have been no confirmed reports of sleeper sharks attacking people. Their environment and behavior make interactions with humans exceedingly rare, thus minimizing any potential danger.

What unique adaptations do sleeper sharks have?

Sleeper sharks have adapted to their deep-sea environment with features like large, oily livers for buoyancy and the ability to produce a natural antifreeze substance in their blood, preventing ice crystal formation in their tissues. Their eyes are also well-adapted to the dark, allowing them to detect bioluminescent prey.

How do sleeper sharks reproduce?

Sleeper sharks are ovoviviparous, meaning they produce eggs that hatch inside the female's body, with the young being born live. This reproductive strategy is advantageous in the deep-sea environment, providing protection to the developing embryos. The gestation period and reproductive cycles of sleeper sharks are not well understood due to the difficulty of studying these elusive creatures.

Discussion Comments

Laotionne

Most sharks that attack humans do so because they mistake the people for another animal, probably a seal. Surfers on their surf boards often look like the outline of seals to sharks attacking from below.

Sporkasia

I am afraid of sharks, yet I am drawn to them as well. And this is not because I have some type of death wish. I would like to go shark cage diving and get a really up close look at the fish. I have done plenty of deep sea diving and I have seen sharks, but I prefer to keep my distance when I am unprotected in the open water. Though I am told that a shark will probably not bother me as long as they are not feeding and excited.

Drentel

Sharks are really exciting creatures. I saw a program on TV recently that talked about several of the different kinds of sharks. I know the great white shark gets most of the press, and I think this is largely because of the way this shark has been seen in movies. If you believe the motion pictures' version of the fish you would think he is the devil in disguise, and you had better not go in the ocean unless you are secured in a shark cage.

Anyway, in the show I watched, the shark that I was most interested in was one of the reef sharks. They can move as fast as 30 miles and hour and they are so agile in the water. Watching them chase and feed on fish gave me a greater appreciation of sharks in general. They are very athletic creatures.

Feryll

When I think about sharks and the animals they prey on, I don't see them snacking on land mammals. I had no idea there was a place where sharks get close enough to land animals to actually kill them. The article mentions that scientist have witnessed these sleeper sharks taking large caribou and eating them. That must be one remarkable sight.

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    • Stomach contents of beached Greenland sharks have been found to contain the remains of animals such as polar bears.
      By: ILYA AKINSHIN
      Stomach contents of beached Greenland sharks have been found to contain the remains of animals such as polar bears.
    • Dolphins sometimes fall prey to Pacific sleep sharks.
      By: crisod
      Dolphins sometimes fall prey to Pacific sleep sharks.
    • Squid are often found in the stomach contents of beached Greenland sharks.
      By: margo555
      Squid are often found in the stomach contents of beached Greenland sharks.